Numerous studies have shown that melatonin can induce sleep in humans. However, the brain mechanisms responsible for this effect are unknown. This is due to the lack of a laboratory rodent model of the soporific effects of melatonin; attempts to induce sleep with melatonin in laboratory rodents have used nocturnal rodents, meaning rodents active during the dark phase of the cycle, such as rats and Djungarian hamsters. Melatonin does not consistently induce sleep in these rodents. In fact, in most of these studies, melatonin reduced sleep and increased wakefulness. Because these nocturnal animals are most active during the night, when melatonin secretion is the highest, these results should not be surprising. A diurnal rodent model is needed to demonstrate the sleep-inducing effects of melatonin. Arvicanthis niloticus (unstriped Nile grass rat), a diurnal murid rodent, is an ideal animal in which to demonstrate the sleep-inducing effects of melatonin. Further, using this rodent as a model, the brain circuitry through which melatonin induces sleep can be investigated. Results from these studies may clarify how melatonin can be used to treat insomnia and